Associative interactions in crowded solutions of biopolymers counteract depletion effects

Joost Groen, David Foschepoth, Esra Te Brinke, Arnold J. Boersma, Hiromi Imamura, Germán Rivas, Hans A. Heus, Wilhelm T.S. Huck*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

36 Citations (Scopus)

Abstract

The cytosol of Escherichia coli is an extremely crowded environment, containing high concentrations of biopolymers which occupy 20-30% of the available volume. Such conditions are expected to yield depletion forces, which strongly promote macromolecular complexation. However, crowded macromolecule solutions, like the cytosol, are very prone to nonspecific associative interactions that can potentially counteract depletion. It remains unclear how the cytosol balances these opposing interactions. We used a FRET-based probe to systematically study depletion in vitro in different crowded environments, including a cytosolic mimic, E. coli lysate. We also studied bundle formation of FtsZ protofilaments under identical crowded conditions as a probe for depletion interactions at much larger overlap volumes of the probe molecule. The FRET probe showed a more compact conformation in synthetic crowding agents, suggesting strong depletion interactions. However, depletion was completely negated in cell lysate and other protein crowding agents, where the FRET probe even occupied slightly more volume. In contrast, bundle formation of FtsZ protofilaments proceeded as readily in E. coli lysate and other protein solutions as in synthetic crowding agents. Our experimental results and model suggest that, in crowded biopolymer solutions, associative interactions counterbalance depletion forces for small macromolecules. Furthermore, the net effects of macromolecular crowding will be dependent on both the size of the macromolecule and its associative interactions with the crowded background.

Original languageEnglish
Pages (from-to)13041-13048
Number of pages8
JournalJournal of the American Chemical Society
Volume137
Issue number40
DOIs
Publication statusPublished - 14 Oct 2015
Externally publishedYes

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